Anyone here has the schematic diagram of the control board for CARRIER indoor unit, Model number, FB4BNF042.
I suspect that the wiring on this control board was incorrect. My neighbor said that a "preventive maintenance" was performed last August and the tech went up the attic and worked on the air register. This guy was passing out flyer for a $50 check-up. I went through his entire unit, this guy missed a loose connection at the condensing unit contactor, causing a burnt power lead wire for the compressor. Tested the 24 VAC contactor test sat. Another incorrect wiring was performed at the thermostat terminal board, the white wire was connected to the "B" terminal and the blue wire was connected to the "W" terminal. When I corrected the wiring the thermostat quit working. This is the contractor type thermostat, non programmabble. Since, i worked as a HVAC tech I have lots of spare thermostat in my truck so I replace it with a new thermostat.During functional test the fuse blows only when the white wire is connected to "W" and operate normally when disconnected. The unit worked flawlessly last winter, now he has issue with the fuse opening @ the indoor unit. While troubleshooting at the indoor unit, I noticed the white wire was connected to the terminal board marked "C" (brown wire) on the control board. Is this suppose to be connected to blue wire, which is common for 24VAC control system? Just trying to help a 86 year old neighbor that has fixed income and cannot afford to pay a tech. I disconnected the white wire at the thermostat, so he can have heat, the heat pump operate fine with this wire disconnected. My e-mail address is firstname.lastname@example.org
. Thanks a lot.